A object floats in a substance while another substance sinks in the same substance. The object's mass and volume is called the density of that particular objects own density and you can actually identify and separate some substances according to their density. There are many laws and principles based on density. We only studied a few of them. We have proved in our class that there is density by pouring a few substances into a jar. We waited for a few moments and the substances formed in separate layers. This is because of the density of the object.